Process for gas phase polymerization

ABSTRACT

A fluidized bed-type polymerization apparatus has an upper blowing equipment installed at a definite height in the fluidized bed area. Through the equipment, a part of the circulating gas and a part, or the whole, of the fresh feed material is blown, thereby to prevent the formation of lumps of polymer in the fluidized bed portion, owing to improved intermixing at the upper portion of the fluidized bed, as well as efficient heat-removal at that portion.

This is a division of application No. 07/968,460, filed Oct. 29, 1992,now U.S. Pat. No. 5,380,494, which was a continuation of 07/773,500filed Oct. 9, 1991 now abandoned.

The present invention relates to an apparatus for fluidized bed-type gasphase polymerization.

In olefin polymerization, recently, yield of polymer against catalystconstituent has been progressively improved owing to a significantimprovement in performance of the polymerization catalysts. Thus, anamount of the residual transition metal catalyst constituent in thepolymer product is diminished, and the catalyst-removing step is able tobe omitted.

Olefin polymerization includes slurry polymerization carried out in aninert hydrocarbon solvent, bulk polymerization carried out in aliquefied monomer such as liquefied propylene, gas phase polymerizationcarried out in a gas phase and the like. Recently, the gas phasepolymerization has come into the limelight, since, besides the progressin the catalyst performance, the solvent recovery and purification stepsare unnecessary and the recovery of monomer and drying of the polymerproduct are easy. At the same time, various kinds of gas phasepolymerization apparatus have come to be utilized.

When a highly effective catalyst is used in the conventional gas phasepolymerization apparatus, however, intermixing of a reaction gas withthe catalyst and the polymer product in the fluidized bed is nothomogeneous. Thus concentrated layers of the highly effective catalystoften tend to be formed in the fluidized bed. Such tendency isparticularly significant, when a large scale apparatus is employed, orwhen an increased amount of the catalyst is fed in order to increase theproduction capacity.

This results in such problems as difficult removal of the heat ofpolymerization reaction, which is liable to form lumps of polymer due tothe locally accelerated polymerization reaction. Stable operation isspoiled and accompanied by inevitable cessation of operation of areactor, and the quality of the polymer product is deteriorated.

An object of the present invention is to provide for a gas phasepolymerization apparatus which is free from such problems as thosecaused by the conventional gas phase polymerization apparatus, namely,which steadily yields polyolefins of excellent quality by preventing theformation of lumps of polymer due to the heterogeneous intermixing inthe fluidized bed.

The present invention relates to a gas phase polymerization reactorprovided with a fluidized bed portion, which is characterized by havinga circulating gas passage at the top of the reactor; a gas chamberprovided at the bottom of the reactor and partitioned by agas-dispersing plate to form an .introducing passage for the circulatinggas and an introducing passage for a fresh feed material; a dischargingpassage for the polymer product provided at the fluidized bed portionabove the gas-discharging plate; a feeding passage for a polymerizationcatalyst; and an upper blowing equipment in order to blow a part of thecirculating gas and/or a part or the whole of the fresh feed material,into the fluidized bed portion, said equipment being located at a heightof l which satisfies the following equations of (1), (2) and (3):

    0<l<L                                                      (1)

    0.4<l/D1.8                                                 (2)

    0.7≦L/D≦2.0                                  (3)

wherein L is height of the fluidized bed; D is inner diameter of thepolymerization reactor; and l is arbitrary height based on thegas-dispersing plate (the L, D and l being units of length).

The present invention also relates to a method for operating such a gasphase polymerization apparatus, which is characterized by introducinginto the upper blowing equipment, 0-20% by weight of the wholecirculating gas and 0-100% by weight of the fresh feed material; and thewhole amount of the material introduced to the upper blowing equipmentis not more than 30% by weight of the whole circulating gas.

The present inventors have found that there was an insufficientlyfluidized zone at a particular area corresponding to a height of Z whichsatisfies the equations (1), (2) and (3) as mentioned above, and haveaccomplished the present invention by improving the state offluidization at that area.

The gas phase polymerization apparatus of the present invention ismainly employed for homopolymerization and copolymerization of olefins,such as ethylene, propylene, butene, pentene, etc.

In the operation of the present apparatus, the most satisfactory stateof fluidization is secured when not less than 80% by weight of the wholecirculating gas is introduced into the circulating gas-introducingpassage at the bottom of the polymerization reactor and not more than20% by weight of the whole circulating gas is introduced into the upperblowing equipment. When the fresh feed material is introduced in theliquid state in the amount corresponding to the amount of the polymerproduced, heat of reaction at the fluidized bed is removed moreeffectively.

The dividing ratio of the fresh feed material to the bottom of thereactor and to the upper blowing equipment may be 0-100% by weight,respectively, to each portion in the liquid state. In other words, thewhole material may be fed at the bottom of the reactor or into the upperblowing equipment. Alternatively, the material may be fed to therespective portions in any ratio.

The gas phase polymerization apparatus of the present invention enablesone to secure the stable state of fluidization of the polymerizationreactor, the homogeneous intermixing even at and around the wall surfaceof the reactor, and thus the prevention of the formation of lumps of thepolymer, by providing an upper blowing equipment in the fluidized bedportion above the plate, at a height of l which satisfies the followingequations:

    0<l<L                                                      (1)

    0.4<l/D≦1.8                                         (2)

    0.7≦L/D≦2.0                                  (3)

wherein L is height of the fluidized bed, D is inner diameter of thereactor, and l is arbitrary height based on the gas-dispersing plate.

Particularly, the present invention makes it easy to design a largescale apparatus which is operated in stable conditions, and also enablesa comparatively simple reorganization of the conventional apparatus,thereby to progressively increase the production capacity by increasingthe feeding amount of catalyst.

Further, if the blowing holes in the upper blowing equipment are soarranged as to allow at least 5% by volume of the blowing gas to blow inthe direction of the wall surface of the polymerization reactor, theintermixing at and around the wall surface is accelerated, thereby thepolymerization reaction progresses more steadily.

Examples according to the present invention will be illustrated belowwith reference to the following Figures.

FIG. 1 shows an exemplified general constitution of a gas polymerizationapparatus equipped with an upper blowing equipment according to thepresent invention.

FIG. 2 shows an exemplified plan of the upper blowing equipmentaccording to the present invention.

FIG. 3 shows a section at A--A' (shown in FIG. 2) of the upper blowingequipment equipped in the gas phase polymirization apparatus accordingto the present invention.

FIG. 3(a) shows an exemplified section of the upper blowing equipment inwhich the section is triangle.

FIG. 3(b) shows an exemplified section of the upper blowing equipment inwhich the section is hexagonal.

FIG. 3(c) shows an exemplified section of the upper blowing equipment inwhich the section is quadrangle.

FIG. 3(d) shows another exemplified section of the upper blowingequipment in which the section is triangle.

FIG. 3(e) shows an exemplified section of the upper blowing equipment inwhich the section is circular.

In these Figures, 1 is a polymerization reactor; is a fluidized bedportion; 3 is an outlet of the circulating gas; 4 is a gas chamber; 5 isan inlet of the circulating gas; 6a, 6b and 6c are introducing passagesfor a fresh feed material; 7 is a gas dispersing plate; 8 is a catalystfeeding passage; 9 is a passage for discharging the polymer product; 10isan upper blowing equipment; 10a is an inlet for the upper blowing gas;11 is a circulating compressor; 12 is a sustaining rod of the upperblowing apparatus.

EXAMPLE 1

In the Examples, a duplicate explanation of elements having the samesymbolwill be ommited, since they have the same function.

The general constitution of a gas polymerization apparatus according tothepresent invention is shown in FIG. 1.

The gas polymerization apparatus in FIG. 1 is constituted from apolymerization reactor 1, a gas-dispersing plate 7 installed in thepolymerization reactor, a gas chamber 4 located beneath, and partitionedby, the gas-dispersing plate 7, a fluidized bed 2 composed of a polymerproduct containing a catalyst and located above the gas-dispersing plate7, a feeding passage 8 for the polymerization catalyst, a passage 9 fordischarging the polymer product, an inlet 5 for the circulating gasconnected to the gas chamber 4, an outlet 3 for the circulating gas fromthe fluidized bed, introducing passages 6a, 6b and 6c for a fresh feedmaterial (the sites a, b and c being settled arbitrarily), an upperblowing equipment 10, and a circulating compressor 11.

The introducing passages 6a, 6b and 6c for the fresh feed material maybe installed at any sites, for example, just before the inlet to the gaschamber 4, just behind the circulating compressor 11, or just before theupper blowing equipment. The circulating gas is mainly introduced fromthepassage for circulating gas connected to the gas chamber 4.

The upper blowing equipment 10 is at a height of l based on thegas-dispersing plate 7, which satisfies the equations (1), (2) and (3)as mentioned above. If it is located at a height which does not satisfythe terms of the equations (1), (2) and (3), the results areunsatisfactory due to the heterogeneous intermixing state at the surfacearea of the fluidized bed portion and thus accelerated formation oflumps of polymer.

The upper blowing equipment 10 is preferably installed along the wallsurface in such a way that the holes of the same equipment 10 blowingagainst the wall surface of the polymerization reactor are located at adistance-less than 1/4 D from the wall surface. The form of the sectionofthe tube in the upper blowing equipment may be circular or polygonal,and the triangle or hexagonal form as set forth in FIG. 3 is preferable.The size of the tube may be selected arbitrarily depending on the amountof gas.

By arranging the gas blowing holes in the upper blowing equipment 10 sothat at least 5% by volume of the whole gas amount blown from the sameequipment 10 is directed upwardly (based on the equipment) and againstthewall surface, the intermixing at and around the wall surface isacceleratedwith satisfactory results. The balance of the gas may bedirected downwardly or to the inner port ion.

As for the amount of the blowing gas from the upper blowing equipment10, at most 20% by weight of the whole circulating gas amount may beblown from the equipment 10. As for the fresh feed material, an amountof an arbitrary ratio of the whole feeding amount may be blown from theequipment 10, and the balance may be introduced along with thecirculatinggas blown into the gas chamber 3 located at the lower portionof the polymerization reactor.

Any shape of the blowing holes installed in the upper blowing equipmentmaybe employed with a similar effects, such as pipe grid (with inclinednozzles), pipe grid (with downward nozzles), slit, bubble cap,perforated plate, perforated nozzle, and the like.

By providing an agitator in the fluidized bed portion of the present gasphase polymerization apparatus, further advantageous effects can beattained. In this case, the agitator may be so arranged that theagitatingblades do not contact to the upper blowing equipment with asuitable lengthof the agitating blade to effect the agitation around theequipment.

EXAMPLES 2-5 AND COMPARATIVE EXAMPLES 1-2

Using a polymerization reactor of 1 m³ volume, arranged according to thepresent invention, propylene polymerization was carried out with thefollowing operating conditions: whole circulating gas of 120 m³ /hr, apressure of 18 kg/cm² G, concentration of propylene of 92% by volume, H₂0.2% by volume, the balance of inert gas, a solid catalystof 1 g/hr,propylene feed of 25 kg/hr, and an average temperature of 80° C.

Ratios of the circulation gas and propylene divided to the upper blowingequipment are shown in Table 1, with the balances being introduced tothe bottom of the polymerization reactor.

                                      TABLE 1                                     __________________________________________________________________________                          Ratio of gas                                                                  introduced                                              No. of                                                                             Ratios of        to the upper                                            Examples                                                                           curculating                                                                            Ratios of                                                                             blowing equip-                                          and  gas      propylene                                                                             ment to the                                             Compar-                                                                            introduced                                                                             introduced                                                                            whole circu-                                            ative                                                                              bottom                                                                            upper                                                                              bottom                                                                            upper                                                                             lating gas                                              examples                                                                           wt %                                                                              wt % wt %                                                                              wt %                                                                              wt %    Remarks                                         __________________________________________________________________________    Ex-2 80  20   75  25  20.1    Steadily                                                                      operable,                                       Ex-3 95   5   25  75  5.1     acompanied                                                                    by no lumps                                     Ex-4 90  10   50  50  10.3    of polymer                                      Ex-5 90  10   100  0  10.0    Continuously                                                                  operable,                                                                     accompanied                                                                   by formation                                                                  of little                                                                     lumps of                                                                      polymer                                         Comp-1                                                                             100  0   100  0  0       Inoperable,                                     Comp-2                                                                             30  70   0   100 70.6    accompanied                                                                   by formation                                                                  of lumps of                                                                   polymer                                         __________________________________________________________________________

As mentioned above, the gas phase polymerization apparatus and themethod for operating the same, according to the present invention,prevents the formation of lumps of polymer in the fluidized bed portion,owing to the improved intermixing at the upper portion of the fluidizedbed, as well asefficient heat-removal at that portion. Thus, a polymerof excellent quality is obtained steadily with a steady operation.

We claim:
 1. A gas phase polymerization process comprising the stepsof:providing a vertically oriented cylindrical polymerization reactor,said reactor having a gas dispersing plate, a gas chamber at the bottomof said reactor, below said gas dispersing plate, and a fluidized bedsection therein, wherein said gas dispersing plate partitions said gaschamber and said fluidized bed section is located above said gasdispersing plate; removing circulating gas from the top of saidpolymerization reactor; introducing a portion of said circulating gas orl portion of said circulating gas and fresh feed material through a gasinlet to said gas chamber; feeding a polymerization catalyst into saidpolymerization reactor through a catalyst inlet defined above said gasdispersing plate; introducing another portion of said circulating gas oranother portion of said circulating gas and fresh feed material throughan upper blowing means into said fluidized bed section of saidpolymerization reactor at a location distinct from and vertically spacedfrom polymerization catalyst inlet, wherein at least 5% by volume of thecirculating gas introduced at height l is blown generally towards aninterior wall of said polymerization reactor, whereby said anotherportion of said circulating gas is introduced within said polymerizationreactor at a height of l which satisfies equations (1), (2) and (3):

    0<l <L                                                     (1)

    0.4≦l/D≦1.8                                  (2)

    0.7≦L/D≦2.0                                  (3)

wherein L is the height from said gas dispersing plate to the top ofsaid fluidized bed section; D is the inner diameter of said cylindricalpolymerization reactor; and l is an arbitrary height from said gasdispersing plate to a location of introduction of said another portionof said circulating gas; and removing a polymer product from thepolymerization reactor.
 2. A gas phase polymerization process comprisingthe steps of:providing a vertically oriented cylindrical polymerizationreactor, said reactor having a gas dispersing plate, a gas chamber atthe bottom of said reactor, below said gas dispersing plate, and afluidized bed section therein, wherein said gas dispersing platepartitions said gas chamber and said fluidized bed section is locatedabove said gas dispersing plate; removing circulating gas from the topof said polymerization reactor; introducing a portion of saidcirculating gas or a portion of said circulating gas and fresh feedmaterial through a gas inlet to said gas chamber; feeding apolymerization catalyst into the polymerization reactor through acatalyst inlet disposed above said gas dispersing plate; introducinganother portion of said circulating gas or another portion of saidcirculating gas and fresh feed material into said fluidized bed portionof said polymerization reactor at a location distinct from andvertically spaced from polymerization catalyst inlet, wherein at least5% by volume of said another portion of said circulating gas introducedat height l is blown generally towards an interior wall of saidpolymerization reactor, whereby said another portion of said circulatinggas is introduced within said polymerization reactor at a height of lwhich satisfies equations (1), (2) and (3):

    0<l<L                                                      (1)

    0.4≦l/D≦1.8                                  (2)

    0.7≦L/D≦2.0                                  (3)

wherein L is the height from said gas dispersing plate to the top ofsaid fluidized bed section; D is the inner diameter of said cylindricalpolymerization reactor; and E is an arbitrary height from the gasdispersing plate to a location of introduction of said another portionof said circulating gas; removing a polymer product from thepolymerization reactor; wherein up to 20% by weight of said circulatinggas and up to 100% by weight of the fresh feed material are introducedat the height l such that the amount of material introduced at theheight l is not more than 30% by weight of the whole circulating gasintroduced into said polymerization reactor.
 3. A gas phasepolymerization process according to claim 1, further comprisingproviding an agitator in the fludized bed portion.
 4. A gas phasepolymerization process process according to claim 3, wherein saidagitator has agitating blades of a length so as to effect agitationaround said upper blowing means without contacting said upper blowingmeans.